Date of Award

2015

Document Type

Open Access Dissertation

Department

Biological Sciences

First Advisor

Johannes W. Stratmann

Abstract

Plants must be able to perceive and properly respond to a multitude of environmental conditions and produce appropriate cellular responses for optimal growth and reproduction. Mitogen-activated protein kinase (MAPK) phosphorylation cascades are critical components of signal transduction networks that mediate cellular responses to a wide range of both biotic and abiotic extracellular stimuli. This thesis presents an investigation of three novel aspects of MAPK signaling, the role of MAPKs in the regulation of cell death, the organization of MAPKs in a multi-protein complex, and the negative regulation of MAPKs by MAPK phosphatases. In tomato, three MAPKs play an essential role in many stress responses. When the genes for all three MAPKs are co-silenced, plants develop a spontaneous, runaway cell death phenotype. Necrotic lesions are associated with strong MAPK silencing, accumulation of catalase, and an elicitor-induced oxidative burst, that is stronger than in control plants. This indicates a novel role of MAPKs in the regulation of programmed cell death. In the second part of this research, a MAPK-containing multi-protein complex was characterized that is involved in the regulation of MAPK dephosphorylation. Typically, only inactive MAPKs associate with the complex. However, when cells were treated with a phosphatase inhibitor, active MAPKs associated with the complex. This suggests the involvement of MAPK phosphatases with the complex. The function of MAPK phosphatases in stress responses was further investigated in Arabidopsis MAPK phosphatase mutants. In these mutants MAPK signaling is altered in response to wounding and a bacterial elicitor, and this correlates with altered defenses to insects and pathogenic bacteria.

Rights

© 2015, Carlton James Bequette

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